This disclosure relates to articles including laminates with a glass substrate that has a film disposed on its surface, and a modified interface between the film and the glass substrate such that the glass substrate substantially retains its average flexural strength, and the film retains key properties for its application.
Articles including a glass substrate, which may be strengthened or strong as described herein, have found wide usage recently as a protective cover glass for displays, especially in touch-screen applications, and there is a potential for its use in many other applications, such as automotive or architectural windows and glass for photovoltaic systems. In many of these applications it can be advantageous to apply a film to the glass substrates. Exemplary films include indium-tin-oxide (“ITO”) or other transparent conductive oxides (e.g., aluminum and gallium doped zinc oxides and fluorine doped tin oxide), hard films of various kinds (e.g., diamond-like carbon, Al2O3, AlN, AlOxNy, Si3N4, SiOxNy, SiAlxOyNz, TiN, TiC), IR or UV reflecting layers, conducting or semiconducting layers, electronics layers, thin-film-transistor layers, or anti-reflection (“AR”) films (e.g., SiO2, Nb2O5 and TiO2 layered structures). In many instances these films must necessarily be hard and/or have a high elastic modulus, or otherwise their other functional properties (e.g., mechanical, durability, electrical conductivity, optical properties) will be degraded. In most cases these films are thin films, that is, they generally have a thickness in the range of 0.005 μm to 10 μm (e.g., 5 nm to 10,000 nm).
When a film is applied to a surface of a glass substrate, which may be strengthened or characterized as strong, the average flexural strength of the glass substrate may be reduced, for example, when evaluated using ball-drop or ring-on-ring strength testing. This behavior has been measured to be independent of temperature effects (i.e., the behavior is not caused by significant or measurable relaxation of surface compressive stress in the strengthened glass substrate due to any heating). The reduction in average flexural strength is also apparently independent of any glass surface damage or corrosion from processing, and is apparently an inherent mechanical attribute of the article, even when thin films having a thickness in the range from about 5 nm to about 10 μm. Without being bound by theory, this reduction in average flexural strength is believed to be associated with the adhesion between such films relative to the strengthened or strong glass substrates, the initially high average flexural strength (or high average strain-to-failure) of selected strengthened or strong glass substrates relative to selected films, together with crack bridging between such a film and the glass substrate. In view of this new understanding, there is a need to prevent films from reducing the average flexural strength of glass substrates.